The Apollo Program Insignia

The Apollo program was a human spaceflight program undertaken by NASA during the years 1961–1975 with the goal of conducting manned moon landing missions. US President John F. Kennedy announced a goal of landing on the moon by the end of the decade in 1961, and it was accomplished on July 20, 1969 by the landing of astronauts Neil Armstrong and Buzz Aldrin, with Michael Collins orbiting above during the Apollo 11 mission. Five other Apollo missions also landed astronauts on the Moon, the last one in 1972. These six Apollo spaceflights are the only times humans have landed on another celestial body. The Apollo program, specifically the lunar landings, is often cited as the greatest achievement in human history. Chronologicaly the manned lunar missions (1969-1972) represent the fifth major mile-stone in the history of space exploration after first sub-orbital flight (1942), first orbital flight (1957), first man in space (1961) and first unmanned lunar mission (1959).

Apollo was the third human spaceflight program undertaken by NASA, the space agency of the United States. It used Apollo spacecraft and Saturn launch vehicles, which were later used for the Skylab program and the joint American-Soviet Apollo-Soyuz Test Project. These later programs are thus often considered to be part of the overall Apollo program.

The goal of the program, as articulated by President Kennedy, was accomplished with only two major failures. The first failure resulted in the deaths of three astronauts, Gus Grissom, Ed White and Roger Chaffee, in the Apollo 1 launchpad fire. The second was an in-space explosion on Apollo 13, which badly damaged the spacecraft on the moonward leg of its journey. The three astronauts aboard narrowly escaped with their lives, thanks to the efforts of flight controllers, project engineers, backup crew members and the skills of the astronauts themselves.

The program set major milestones in the history of human spaceflight. This program stands alone in sending manned missions beyond low Earth orbit. Apollo 8 was the first manned spacecraft to orbit another celestial body, while Apollo 17 marks the time of the last moonwalk and also the last manned mission beyond low Earth orbit.

The program spurred advances in many areas of technology peripheral to rocketry and manned spaceflight. These include major contributions in the fields of avionics, telecommunications, and computers. The program sparked interest in many fields of engineering, including pioneering work using statistical methods to study the reliability of complex systems made from component parts. The physical facilities and machines which were necessary components of the manned spaceflight program remain as landmarks of civil, mechanical, and electrical engineering. Many objects and artifacts from the program are on display at various locations throughout the world, notably at the Smithsonian's Air and Space Museums.


President John F. Kennedy delivers a speech at Rice University on the subject of the American space program, September 12, 1962.

The Apollo program was originally conceived early in 1960, during the Eisenhower administration, as a follow-up to America's Mercury program. While the Mercury capsule could only support one astronaut on a limited earth orbital mission, the Apollo spacecraft was intended to be able to carry three astronauts on a circumlunar flight and perhaps even on a lunar landing. The program was named after the Greek god of light and archery by NASA manager Abe Silverstein, who later said that "I was naming the spacecraft like I'd name my baby." While NASA went ahead with planning for Apollo, funding for the program was far from certain, particularly given Eisenhower's equivocal attitude to manned spaceflight. In November 1960, John F. Kennedy was elected President after a campaign that promised American superiority over the Soviet Union in the fields of space exploration and missile defense. Using space exploration as a symbol of national prestige, he warned of a "missile gap" between the two nations, pledging to make the U.S. not "first but, first and, first if, but first period." Despite Kennedy's rhetoric, he did not immediately come to a decision on the status of the Apollo program once he was elected President. He knew little about the technical details of the space program, and was put off by the massive financial commitment required by a manned moon landing. When NASA Administrator James Webb requested a thirty percent budget increase for his agency, Kennedy supported an acceleration of NASA's large booster program but deferred a decision on the broader issue.

On April 12, 1961, Soviet cosmonaut Yuri Gagarin became the first man to fly in space, reinforcing American fears about being left behind in a technological competition with the Soviet Union. At a meeting of the U.S. House Committee on Science and Astronautics held only one day after Gagarin's flight, many congressmen pledged their support for a crash program aimed at ensuring that America would catch up. Kennedy, however, was circumspect in his response to the news, refusing to make a commitment on America's response to the Soviets. On April 20 Kennedy sent a memo to Vice President Lyndon B. Johnson, asking Johnson to look into the status of America's space program, and into programs that could offer NASA the opportunity to catch up. Johnson responded on the following day, concluding that "we are neither making maximum effort nor achieving results necessary if this country is to reach a position of leadership." His memo concluded that a manned moon landing was far enough in the future to make it possible that the United States could achieve it first.

On May 25, 1961, Kennedy announced his support for the Apollo program as part of a special address to a joint session of Congress:

First, I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth. No single space project in this period will be more impressive to mankind, or more important in the long-range exploration of space; and none will be so difficult or expensive to accomplish.

John F. Kennedy

At the time of Kennedy's speech, only one American had flown in space — less than a month earlier — and NASA had not yet sent a man into orbit. Even some NASA employees doubted whether Kennedy's ambitious goal could be met.

Answering President Kennedy's challenge and landing men on the moon by the end of 1969 required the most sudden burst of technological creativity, and the largest commitment of resources ($25 billion), ever made by any nation in peacetime. At its peak, the Apollo program employed 400,000 people and required the support of over 20,000 industrial firms and universities.

We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.

John F. Kennedy

Choosing a mission mode

Once Kennedy had defined a goal, the Apollo mission planners were faced with the challenge of designing a set of flights that could meet this stated goal while minimizing risk to human life, cost, and demands on technology and astronaut skill. Four possible mission modes were considered:

  • Direct Ascent: A spacecraft would travel directly to the Moon, landing and returning as a unit. This plan would have required a very powerful booster, the planned Nova rocket.
  • Earth Orbit Rendezvous (EOR): Multiple rockets (up to fifteen in some claims) would be launched, each carrying various parts of a Direct Ascent spacecraft and propulsion units that would have enabled the spacecraft to escape earth orbit. After a docking in earth orbit, the spacecraft would have landed on the Moon as a unit.
  • Lunar Surface Rendezvous: Two spacecraft would be launched in succession. The first, an automated vehicle carrying propellants, would land on the Moon and would be followed some time later by the manned vehicle. Propellant would be transferred from the automated vehicle to the manned vehicle before the manned vehicle could return to Earth.
  • Lunar Orbit Rendezvous (LOR): One Saturn V would launch a spacecraft that was composed of modular parts. A command module would remain in orbit around the moon, while a lunar module would descend to the moon and then return to dock with the command module while still in lunar orbit. In contrast with the other plans, LOR required only a small part of the spacecraft to land on the Moon, thereby minimizing the mass to be launched from the Moon's surface for the return trip.

In early 1961, direct ascent was generally the mission mode in favor at NASA. Many engineers feared that a rendezvous -- let alone a docking -- neither of which had been attempted even in Earth orbit, would be extremely difficult in lunar orbit. However, dissenters including John Houbolt at Langley Research Center emphasized the important weight reductions that were offered by the LOR approach. Throughout 1960 and 1961, Houbolt campaigned for the recognition of LOR as a valid and practical option. Bypassing the NASA hierarchy, he sent a series of memos and reports on the issue to Associate Administrator Robert Seamans; while acknowledging that he spoke "somewhat as a voice in the wilderness," Houbolt pleaded that LOR should not be discounted in studies of the question.

Seamans' establishment of the Golovin committee in July 1961 represented a turning point in NASA's mission mode decision. While the ad-hoc committee was intended to provide a recommendation on the boosters to be used in the Apollo program, it recognized that the mode decision was an important part of this question. The committee recommended in favor of a hybrid EOR-LOR mode, but its consideration of LOR — as well as Houbolt's ceaseless work — played an important role in publicizing the workability of the approach. In late 1961 and early 1962, members of NASA's Space Task Group at the Manned Spacecraft Center in Houston began to come around to support for LOR. The engineers at Marshall Space Flight Center took longer to become convinced of its merits, but their conversion was announced by Wernher von Braun at a briefing in June 1962. NASA's formal decision in favor of LOR was announced on July 11, 1962. Space historian James Hansen concludes that:

Without NASA's adoption of this stubbornly held minority opinion in 1962, the United States may still have reached the Moon, but almost certainly it would not have been accomplished by the end of the 1960s, President Kennedy's target date.

James Hansen


The decision in favor of lunar orbit rendezvous dictated the basic design of the Apollo spacecraft. It would consist of two main sections: the Command/Service Module (CSM), in which the crew would spend most of the mission, and the Lunar Module (LM), which would descend to and return from the lunar surface.

Command/service module

Apollo CSM in lunar orbit.

The command module (CM) was conical in shape, and was designed to carry three astronauts from launch into lunar orbit and back from the moon to splashdown. Equipment carried by the command module included reaction control engines, a docking tunnel, guidance and navigation systems and the Apollo Guidance Computer. Attached to the command module was the service module (SM), which housed the service propulsion system and its propellants, the fuel cell power system, four maneuvering thruster quads, the S-band antenna for communication with Mission Control, and storage tanks for water and air. On Apollo 15, 16 and 17 it also carried a scientific instrument package. The two sections of the spacecraft would remain attached until just prior to re-entry, at which point the service module would be discarded. Only the command module was provided with a heat shield that would allow it and its passengers to survive the intense heat of re-entry. After re-entry it would deploy parachutes that would slow its descent through the atmosphere, allowing a smooth splashdown in the ocean.

Under the leadership of Harrison Storms, North American Aviation won the contract to build the CSM for NASA. Relations between North American and NASA were strained during the Apollo program, particularly after the Apollo 1 fire during which three astronauts died. The cause of the accident was determined to be an electrical short in the wiring of the command module; while determination of responsibility for the accident was complex, the review board concluded that “deficiencies existed in Command Module design, workmanship and quality control.”

Lunar module

The Lunar Module (LM) (also known as Lunar Excursion Module, or LEM), was designed solely to land on the moon, and to ascend from the lunar surface to the command module. It had a limited heat shield and was of a construction so lightweight that it would not have been able to fly in Earth gravity. It carried two crewmembers and consisted of two stages, a descent and an ascent stage. The descent stage incorporated compartments in which cargo such as the Apollo Lunar Surface Experiment Package and Lunar Rover could be carried.

Apollo LM on lunar surface

The contract for design and construction of the lunar module was awarded to Grumman, and the project was overseen by Tom Kelly. There were also problems with the lunar module; due to delays in the test program, the LM became what was known as a "pacing item," meaning that it was in danger of delaying the schedule of the whole Apollo program. Due to these issues, the Apollo missions were rescheduled so that the first manned mission with the lunar module would be Apollo 9, rather than Apollo 8 as was originally planned.


When the team of engineers led by Wernher von Braun began planning for the Apollo program, it was not yet clear what sort of mission their rocket boosters would have to support. Direct ascent would require a booster, the planned Nova rocket, which could lift a very large payload. NASA's decision in favor of lunar orbit rendezvous re-oriented the work of Marshall Spaceflight Center towards the development of the Saturn 1B and Saturn V. While these were less powerful than the Nova would have been, the Saturn V was still much more powerful than any booster developed before—or since.

Saturn V

The Saturn V consisted of three stages and an Instrument Unit which contained the booster's guidance system. The first stage, the S-IC, consisted of five F-1 engines arranged in a cross pattern, which produced a total of 7.5 million pounds of thrust. They burned for only 2.5 minutes, accelerating the spacecraft to a speed of approximately 6000 miles per hour (2.68 km/s). During development, the F-1 engines were plagued by combustion instability—if the combustion of propellants was not uniform across the flame front of an engine, pressure waves could build which would cause the engine to destroy itself. The problem was solved in the end through trial and error, fine-tuning the engines through numerous tests so that even small charges set off inside the engine would not induce instability.

The second stage, the S-II, used five J-2 engines. They burned for approximately six minutes, taking the spacecraft to a speed of 15,300 miles per hour (6.84 km/s) and an altitude of about 115 miles (185 km). At this point the S-IVB third stage took over, putting the spacecraft into orbit. Its one J-2 engine was designed to be restarted in order to make the translunar injection burn.

Missions of the Apollo program
Rocket tests
SA-1 · SA-2 · SA-3 · SA-4 · SA-5 · AS-203 (Apollo 2)
Abort tests
QTV · Pad Abort Test-1 · A-001 · A-002 · A-003 · Pad Abort Test-2 · A-004
Boilerplate tests
A-101 · A-102 · A-103 · A-104 · A-105
Unmanned missions
AS-201 · AS-202 (Apollo 3) · Apollo 4 · Apollo 5 · Apollo 6 · Skylab 1
LEO missions
AS-204 (Apollo 1) · Apollo 7 · Apollo 9 · Skylab 2 · Skylab 3 · Skylab 4 · Apollo-Soyuz Test Project
Lunar missions